Best way to protect a public folder

none of the above except for the server OS.
this is done all the time and accomplished by setting share right/folder rights via the server file system.

The point is to be user-friendly so anyone without any sharing / security knowledge could create an account for a user. Like a software that could do this. Also, if it could be done remotely. Think about an internet station where people just want to have their private folders.

Who would go in compmgmt.msc to give a user a standard access...?

More ideas?

Your request doesn't really make sense...I want it secure, but I want it easy enough for anyone to create accounts. First thing about security is reducing the number of people that could create an account. If this is on a network and the server is NOT available on the internet, then create an account for each user on the server, create your shares, then establish your permissions for what the users can and cannot do. If it's available from outside the network, then you'll want to use a higher level of security to make sure your data doesn't get compromised or the server doesn't get hacked/compromised. What ultimately are you trying to accomplish and perhaps more specific recommendations could be provided.